The present invention relates to a motor vehicle radar system.
Motor vehicle radar systems are used, for example, in the context of a vehicle automatic speed control for detecting vehicles traveling ahead. One system is also termed Adaptive Cruise Control (ACC). In order to influence the electromagnetic waves used and thus also to protect the radar system from atmospheric conditions, a body is usually located in the beam path of the electromagnetic waves. Often this body is a component of a housing that surrounds a motor vehicle radar system of this type.
In German Patent No. 197 36 089, a metal plate lens is described, which is used for focusing or dispersing electromagnetic waves. The metal plate lens described is used preferably in a motor vehicle radar system. German Patent No. 197 36 089, is based on the consideration that, in the context of a radar system for automatic distance warning in a motor vehicle, specific conditions of use result in covering deposits, especially of snow or slush, building up on the lens. As a result of deposits of this type, electromagnetic waves passing through the lens are substantially dampened, which can ultimately lead to the total failure of the radar system. To improve the metal plate lens with regard to the aforementioned difficulties, it is proposed that, in at least one of the metal plates, there is a contact which can supply a heating current to the metal plate. In this context, the aforementioned metal plate can be connected in an electrically conductive manner to further metal plates of the lens, so that a supplied heating current also flows through the further metal plates. The aforementioned metal plate and the further metal plates can be connected to each other in series, in parallel, or in another switchable combination. So that the metal plate lens can also simultaneously function as a weather-proof covering for the actual motor vehicle radar system, the space between the metal plates of the metal plate lens is filled with a solid or foam dielectric. To increase the heating power, the metal plates to which a heating current can be supplied have a partial area which has an increased specific ohmic resistance in comparison to copper. This specific ohmic resistance increases the power loss, which results in greater heating power and therefore in a more powerful heating of the antenna lens.
From German Patent No. 196 44 164, a motor vehicle radar system is known that has at least one transmitting/receiving element for transmitting and/or receiving electromagnetic waves, a lens-shaped dielectric body being disposed in the beam path of the at least one transmitting/receiving element for focusing or dispersing the electromagnetic waves. The lens-shaped dialectic body, which also protects the transmitting/receiving element from atmospheric conditions, has an arrangement made of electrically conductive printed circuit traces, whose width, at a maximum, constitutes a tenth-wave, and whose distances from each other, at a minimum, constitute a quarter-wave, lambda designating the free-space wavelength of the electromagnetic waves. The electrically conductive printed circuit traces, in this context, are arranged so as to be predominantly perpendicular to the polarization direction of the electromagnetic waves. The arrangement composed of electrically conductive printed circuit traces, in accordance with the desired application, can be disposed on the inner side of the dielectric body, i.e., the side that is facing the transmitting/receiving elements, the outer side, or even within the dielectric body. If a heating current flows through the electrically conductive arrangement, the dielectric body can in this manner be freed from deposits such as ice, snow, or slush. Similarly, using a heating current, the dielectric body can be dried or can be kept dry. Furthermore, it is disclosed that the possibility exists to subdivide the electrically conductive arrangement into at least two components, that are separated from each other. In this constellation, if the arrangement composed of electrically conductive printed circuit traces is situated on the outer side of the dielectric body, it is possible, by measuring the capacitance between the two separated components of the arrangement, to arrive at conclusions as to a so-called loss angle tan xcex4 of the coating material. In other words, it is possible to establish a contamination of the dielectric body. As a function of this established contamination, or of an established dirt covering, a heating current, which flows through the electrically conductive arrangement, can be switched on. On the other hand, by being subdivided into at least two areas, the heating power can be varied, for example, for a rapid heating up of an ice-covered lens using high heating power and subsequently keeping the lens free using reduced heating power. From German Patent No. 196 44 164, it is also known that the electrical printed circuit traces, in a ceramic body, are applied using a known thick-film technology, whereas in bodies made of plastic, cost-effective methods, that are also known, can be used for imprinting the electrical printed circuit traces.
German Published Patent Application No. 197 24 320 discloses a method for manufacturing a heatable antenna lens. A heatable antenna lens made of a dielectric body is described, which contains within it an arrangement made of electrical printed circuit traces. In this context, the arrangement made of electrically conductive traces is situated as close as possible to the outer surface of the lens to be heated, as a result of which there is a reduction in the heating power by applying the energy closely underneath the surface to be heated. In addition, accelerated heating-up behavior results from this. It is also described that it is possible to achieve an efficient adjustability of the heating power as a result of the fact that wires are used that have a desired resistance behavior. This can be, for example, a resistance wire.
Both German Patent No. 197 36 089, and German Patent No. 196 44 164 as well as German Published Patent Application No. 197 24 320 describe various possibilities for freeing a motor vehicle radar system from coatings of ice, snow, or slush. The two first cited documents disclose the possibility of regulating the heating power as a result of the fact that either the metal plates are connected to each other in various combinations or at least two electrically conductive arrangements are combined for regulating the heating power accordingly. German Published Patent Application No. 197 24 320, on the other hand, discloses only the possibility of adjusting the heating power using wires having a desired resistance behavior. In the aforementioned systems, at lower external temperatures and at higher driving speeds, the result is a powerful cooling of the surface due to the convection at the surface of the radar system. In this context, depending on the ambient conditions and the driving speed, it is possible that despite a switched-on maximum heating power, temperatures at the surface of the radar system can be close to the freezing point.
The object of the present invention lies in indicating a motor vehicle radar system that is better adapted to the ambient conditions. This objective is achieved as a result of the fact that in a motor vehicle radar system having at least one sensor-radiation transparent body for focusing the sensor beam and/or a radome without the desired focusing in the beam path, at least one arrangement made of electrical printed circuit traces being disposed in the area of the sensor-radiation transparent body and/or the radome, the arrangement being appropriate at least for heating the sensor-radiation transparent body and/or the radome, it being possible to supply electrical power to the electrical printed circuit traces, power control of the supplied electrical power being carried out as a function of the operating states and ambient conditions, such that the surface temperature of the sensor-radiation transparent body and/or of the radome does not exceed preestablished temperature values. In this context, the sensor-radiation transparent body is advantageously a dielectric lens, thus making possible a particularly compact design.
In contrast to the systems known from the related art, the motor vehicle radar system according to the present invention offers the advantage that power control is carried out for the supply of electrical power and is made a function of not only on a possibly detected degree of soiling but rather on operating states and ambient conditions. In this context, the power control according to the present invention is designed such that the surface temperature of the sensor-radiation transparent body and/or the radome does not exceed predetermined temperature values. As a result, the sensor-radiation transparent body and/or the radome is prevented from being damaged by impermissibly high temperature values.
The preferred embodiment of the motor vehicle radar system according to the present invention provides that power control is accomplished as a result of the fact that a dropping voltage on the electrical printed circuit traces is not constant over time. According to the present invention, this can result from the fact that the voltage is a fundamental voltage that is clocked by a switch at a preestablished pulse-duty factor. Advantageously, the operating voltage of the vehicle electrical system is used as the fundamental voltage. This embodiment of the power control according to the present invention offers the advantage that, on the one hand, via a preestablished pulse-duty factor, the temporal average value of the supplied electrical power can be precisely controlled and that, on the other hand, as the clocked fundamental voltage the operating voltage is used, which is permanently available in the vehicle electrical system without further transformation or conversion.
It is of special advantage if the voltage is a function of at least one of the following operating states and/or one of the following ambient conditions:
1. the operating voltage of the motor vehicle electrical system,
2. the ambient temperature outside the motor vehicle,
3. the speed of the motor vehicle itself, and
4. the surface temperature of the sensor-radiation transparent body and/or the radome.
As a result of one or a plurality of the aforementioned parameters, the voltage dropping off at the electrical printed circuit traces is adjusted in a particularly advantageous manner to the operating states and/or ambient conditions. It is also advantageous if at least one of the aforementioned quantities is available on a vehicle-internal bus system, for example, the CAN bus, because, in this manner, it is possible to fall back on measuring quantities which are already available inside the vehicle system, and as a result, no additional measuring data and/or sensors are necessary.
Determining the aforementioned pulse-duty factor can be carried out by a control unit, there being advantageously present in the control unit a memory, in which an input-output map can be stored. In this manner, during the operation of the motor vehicle radar system, no calculation-intensive operations are necessary to determine the pulse-duty factor of the voltage, but rather a corresponding value for the pulse-duty factor has only to be read out from an input-output map stored in the memory as a function of preestablished operating states and/or ambient conditions. This is a particularly rapid, cost-effective, and very precise way to determine the pulse-duty factor.
In the motor vehicle radar system according to the present invention, it is also provided to measure the operating voltage of the vehicle electrical system using an analog-digital converter, which, together with the control unit, can be integrated in a radar system control unit. In this manner, the actual operating voltage of the vehicle electrical system can be measured, which, e.g., after a long period of standing at low ambient temperatures, can significantly deviate from values that the operating voltage of the vehicle electrical system has, for example, at moderate external temperatures and after long highway travel. Having knowledge of the operating voltage of the vehicle electrical system, determined in this manner, a particularly exact power control can be carried out.
A particularly advantageous embodiment of the motor vehicle radar system provides that the arrangement made of electrical printed circuit traces is dimensioned such that the electrical resistance of the electrical printed circuit traces is so small that in response to a lasting pulse-duty factor of 1, a multiple of the actually permissible heating power results. In other words, the electrical printed circuit traces are designed from the point of view of their electrical resistance, such that a long-term operation at maximum fundamental voltage, or operating voltage of the vehicle electrical system, would lead to unacceptably high heating power and therefore to the destruction of the motor vehicle radar system. As a result of this type of design of the electrical printed circuit traces, it is possible, on a short-term basis, to supply to the motor vehicle radar system power which, if used on a long-term basis, would result in destruction. In this manner, a more rapid, particularly advantageous heating-up behavior of the motor vehicle radar system is achieved.
A further embodiment of the motor vehicle radar system provides that the arrangement of the electrical printed circuit traces is made of a ferromagnetic material. A ferromagnetic material of this type offers the advantage that, as a result of the positive temperature coefficient of the material, the motor vehicle radar system is self-protected from overheating. Furthermore, ferromagnetic material, especially in a latticed arrangement, offers the advantage that low-frequency interference radiation is suppressed especially efficiently. This can relate to both the entry as well as the exit of interference radiation.